Potential Carlin-Style Gold Belt
“Mapimí Gold Corridor” may be a new Carlin-style Gold Belt
Through 2021 and 2022 Southern Empire has acquired interests in four projects in northern México. These include a string of three gold projects with bulk-tonnage scale potential extending 165 km along the proposed, southeast trending, Oligocene tectonostratigraphic Mapimí Gold Corridor:
● Centauro Gold Project, Escalón, Chihuahua State
● Pedro Gold Project, Mapimí, Durango State
● La Loma Gold Project, Nazas, Durango
“The idea that there could be a metallogenic trend of bulk-minable, sediment-hosted gold deposits in north-central México makes for a very compelling exploration strategy….with the Synchrotron Micro-XRF analyses of Pedro drill core specimens, we have strong mineralogical evidence that further supports the classification of the Pedro gold mineralization as “Carlin-style”, an important concept that will be applied to our exploration modelling.”
Dale Wallster, Southern Empire’s CEO
The postulated Mapimí Gold Corridor is highlighted in part by the occurrence of gold and a suite of specific indicator elements present at Southern Empire’s Centauro, Pedro and La Loma properties. At Centauro and Pedro and, to an extent, the lesser studied La Loma, a range of similar, specific geological, mineralogical, alteration and geochemical features are present supporting the possibility of the Mapimí Gold Corridor being a metallogenic belt hosting Carlin-style gold deposits. The Mapimí Gold Corridor is situated along the northwestern end of the Sierra Madre Oriental mountain range where Cretaceous carbonate stratigraphy of the Mexican Fold and Thrust Belt has undergone east-west Oligocene extension related to development of the México Basin and Range physiographic province. The Mapimí Gold Corridor is also host to significant precious and base metal Carbonate Replacement Deposits (“CRD”; eg. Ojuela, Platosa) and epithermal deposits.
The Centauro, Pedro, and La Loma Gold Projects occur within a belt of Cretaceous limestone, sandstone and mudstone lithologies exposed along the northern portions of the 2,000 km-long Mexican Fold and Thrust Belt (“MFTB”), a thin-skinned, orogenic tectonic wedge of both Seier and Laramide orogenic associations. Kilometre-scale, brittle thrust faults dominate deformation of these platform carbonate rocks, while more ductile, mesoscopic buckle folds and associated cleavage dominate deformation in the basinal carbonates (Fitz-Diaz et al, 2012). The overall trend of the MFTB is NW-SE, except through the east-west Transverse Sierras Sub-province, part of a primary, oroclinal fold from the western hinge of which the Mapimí Gold Corridor extends.
During the Oligocene Epoch, while subduction of the Farallon Plate remained active, east-west extension began along the eastern margins of the Sierra Madre Occidental, including all of the northwest end of the MFTB and east through the Transverse Sierra Sub-province, forming the Mexican “Basin and Range” physiographic province (Ferrari et al, 2007).
The Mapimí Gold Corridor aligns with north-northwest trending grabens related to the Oligocene extension, as do various Eocene to Oligocene age intrusives of granodiorite to monzonite and volcanic eruptive centres of predominantly rhyolitic ignimbrite. Centauro is spatially associated with an Eocene monzonite intrusion and the Pedro region includes multiple Oligocene granodiorite plugs and plutons. Graben structures throughout the eastern sections of Mexican Basin and Range province are also associated with limestone-dominated polymictic conglomerates and basinal sediments of the Eocene to Oligocene Ahuichila Formation.
The Centauro, Pedro and La Loma properties additionally highlight the tectonostratigraphic-defined Mapimí Gold Corridor that includes thick fold and fault repeated Cretaceous carbonate stratigraphy, north-northwest trending graben structures of the Oligocene Mexican Basin and Range province and linearly associated Eocene to Oligocene centres of intrusive activity and limestone conglomerates. The characteristics of
exploration interest include:
● anomalous gold (“Au”); silver (“Ag”) low to absent);
● anomalous regional arsenic (“As”), mercury (“Hg”), antimony (“Sb”), thallium (“Tl”) and fluoride (“F”)
geochemistry (lead (“Pb”), zinc (“Zn”), copper (“Cu”) low to absent); and,
● pervasive silica and clay alteration.
The regional setting of the Mapimí Gold Corridor is associated with numerous, specific geological, mineralogical and geochemical characteristics observed at Centauro, Pedro and La Loma that strongly support the proposition that the Mapimí Gold Corridor has significant potential to host a bulk-minable, Carlin-style gold deposit.
Applied to Centauro and Pedro specifically, and to a lesser extent La Loma, the Mapimí Gold Corridor compares favourably on the above checklist of “Carlin-style” characteristics adapted from Muntean & Cline (2018).
The geology of the Pedro and Centauro properties (those being the best studied), provides numerous examples to support this conclusion, not the least being late-stage orpiment and realgar mineralization observed in silicified, brecciated Ahuichila Formation limestone conglomerates.
Mineralogical studies using a Synchrotron Micro-XRF to map constituent pyrite grains were completed in 2022 on specimens from Pedro drill hole P22-02 (46.0m to 47.4m) by LISA CAN, in collaboration with Western University (see image below)
Synchrotron radiation micro-X-Ray fluorescence (SRμ-XRF) was conducted by LISA CAN on representative pyrite grains in sample SER-2B. The LISA CAN study, with its exceptional sampling capability (<2μm spot size) provides further support for Pedro mineralization being “Carlin-style” in that:
● Trace elements Hg and Tl were associated with pyrite grains.
● Hg and Tl occur together in the arsenical rim of pyrite grain SER-2B-1-1.
● No gold was identified.
○ Hg and Tl are not associated with one another
○ Hg is heterogeneously distributed in most pyrites
○ Sb was not identifiable due to overlap between diagnostic of XRF emission peaks for it and
As observed at both Centauro and Pedro, gold mineralization is predominantly associated with hematite- stained, weak to moderately silicified brecciated limestone conglomerates of the Eocene to Oligocene Ahuichila Formation. The Ahuichila Fm. is a predominately limestone, heterolithic conglomerate associated with NNW trending graben structures (sandstone, tuffaceous sandstone and conglomerates) that stratigraphically overlies the Late Cretaceous to Eocene Caracol Formation.
The silicified auriferous breccia zones are typically linear, following probable NNW structures. The silicified conglomerate zones at both Centauro and Pedro are highlighted by kilometre-scale, coincident geochemical soil anomalies of Au (>10 ppb), As (>100 ppm), plus Sb, Th, Hg & Ba.
Further detailed discussions of the Centauro, Pedro and La Loma properties following provide further details in support of the conclusions that the Mapimí Gold Corridor has the potential to host a bulk-minable Carlin-style gold deposit.
A study designed to map potential impacts to human health from naturally occurring arsenic and fluoride in water (groundwater and surface water) throughout northwest México was undertaken in 2017 (Alacon-Herrera et al, 2019). Although the study was designed for a very different purpose, and the reported data is sparse and incomplete suite of chemical elements is reported, naturally occurring As and F geochemical signatures clearly identify eastern Chihuahua and Durango as As and F anomalous regions. This further supports the concept of a potential gold-endowed metallogenic province in eastern Chihuahua and Durango states.
Irrespective of the assumptions made in the study about the source of As and F in water in the region, the presence of highly anomalous As and F deposit areas as identified in Centauro, Pedro and likely La Loma seem more than just coincidental to the naturally high levels of As and F mapped in water samples in the region by this study.
The above figure shows As and F concentrations from groundwater and surface water sources sampled in 2017 throughout northwest México (14,058 samples taken from 3,951 sources), as reported by Alacon- Herrera et al, 2019 in the human health study. Only sites at or above human health limits are plotted; 639 of 5,951 sites (16.2%) had As values above the human health limit of 10 μg/L As, and 184 of 3,951 sites (3.8%) were above the human health limit of 1500 μg/L F. Anomalous sites are predominantly located in the arid plateaus of eastern Chihuahua, Durango and Zacatecas states. The study attributes the arid climate of the central Mexican plateau as key to the perseverance of As and F in the environment and proposes that Oligocene to Miocene felsic volcanic rocks of the Sierra Madre Occidental are a contributing source.
Access and infrastructure along the majority of the Mapimí Gold Corridor is good, with federal toll highway 490 and state highway 49, the FerroMex main rail line and 230 kV NORMX electrical transmission power lines running the length of its eastern boundary. Pedro is accessed from state highway 30 running west through Mapimí. All 3 project areas are within a 1.5-hour drive of the sister cities of Gomez Palacio, Durango and Torreon, Coahuila, a major manufacturing and transportation hub with reliable regional air service and excellent medical facilities.